In this type of assembly, the tensioner goes from its idle position to its operating position according to the following steps.
In the idle position, the tensioner is separated from the belt (no contact).
The tensioner is rotated in this predefined rotation direction (for example, counterclockwise direction) until it is in contact with the belt (point of contact).
One then continues to rotate the tensioner in this predefined rotation direction, generally using a tool. The belt then exerts a force on the tensioner, in reaction to the force applied by the tensioner thereon, which tends to push the tensioner back toward its idle position. This force therefore tends to rotate the tensioner in the direction opposite the predefined rotation direction (therefore in the clockwise direction if we use the same example).
One then continues to rotate the tensioner in the predefined rotation direction until reaching a tilting point.
Below this tilting point, the reaction force exerted by the belt increases and tends to return the tensioner toward its idle position, while still acting in the direction opposite the predefined rotation direction.
However, past this tilting point, the force exerted by the belt on the tensioner acts to rotate the tensioner in the predefined rotation direction (counterclockwise if we use the same example). Thus, past the tilting point, it is no longer necessary to exert a force to rotate the tensioner in the predefined rotation direction, since the assembly itself acts automatically to tilt the tensioner from the tilting position toward the operating position.
A stop is then provided to prevent the tensioner from rotating in the predefined rotation direction past its operating position. The stop therefore defines the operating position of the tensioner.
The tilting point is sometimes called a “toggle point”. For this reason, this assembly is sometimes described as “overtoggling”.
This type of assembly is particularly interesting because it makes it possible to place the tensioner in its operating position easily, with a tool (lever arm, for example) that can be actuated with one hand. Once the toggle point is reached, everything happens automatically, with no additional effort for the installer. It is especially used with the elastic belts, for which it is easier to reach the toggle point.
Such an assembly is for example proposed in document EP 1,317,635.
The plate of the tensioner is mounted here on the stationary support (engine block) by means of a fixed pivot axis. On this pivot axis, both the fastening of the tensioner on the stationary support and the pivot function allowing the tensioner to pivot relative to the stationary support are performed.
The articulation means is therefore complex.
Furthermore, in order to ensure that the assembly will be able to allow the passage of the tensioner past the toggle point, the pivot axis must be installed carefully on the stationary support, the tensioner defining, in its travel between its idle position and its operating position, an arc of circle.
This installation is not always easy, since it requires leaving space for the tensioner in its installation travel.
It is even sometimes impossible due to the local bulk, related to other design constraints relative to the engine block.